1. Field of the Invention
This invention relates to solder material having an excellent heat fatigue resistance in a solder joining portion when an electronic component is joined to a substrate using the solder material, and an electronic part using the same.
2. Description of the Prior Art
Currently solder material is used for joining the IC chip, capacitor or the like to a substrate and eutectic solders essentially consisting of 5% by weight of Sn and 95% by weight of Pb or 63% by weight of Sn and 37% by weight of Pb are used.
On the other hand, when the IC chip, capacitor or the like is joined to the substrate using the solder material, usually film of Ni, Cu or the like is interposed therebetween.
The substrate having the IC chip or the like, incorporated in electronic apparatus is exposed to temperature cycle environment in which heating and cooling are repeated with ON/OFF of the electronic apparatus. Particularly with current trend of decreased size and thickness of its packages, there is produced such a problem that when the solder joined portion is exposed to temperature cycle environment, cracks are likely to occur. The reason is that although a measure against cracks was taken by design change of the mounting style according to the prior art, with the decreased size and thickness of the package, the freedom of mounting style design is limited so that the aforementioned measure is impossible to do.
Therefore, solder material not causing crack even if exposed to temperature cycle environment has been demanded.
To meet such a demand, for example, Japanese Unexamined Patent Application No. Hei 1-127192 has disclosed that by mixing a predetermined amount of tellurium with Sn--Pb alloy, anti-crack characteristic is improved. Further, Japanese Unexamined Patent Application No. Hei 1-237095 has disclosed that by mixing a predetermined amount of Sb and In with the Sn--Pb alloy, the anti-crack characteristic is improved. Japanese Unexamined Patent Application No. Hei 7-299585 has disclosed that by mixing a predetermined amount of Sb and Ni with the Sn--Pb alloy, the fatigue resistance is improved.
However, when the IC chip or the like is joined to the substrate by the aforementioned conventional solder material, the heat fatigue resistance of the solder material exposed to temperature cycle environment is demanded to be further improved.
Further, if the Ni film is interposed to improve the joining performance of the solder material, a solder material capable of reducing damage of such Ni film is demanded.